The effect of different Na 2 O and K 2 O ratios of alkali activator on compressive strength of fly ash based-geopolymer

Leong, Hsiao Yun; Ong, Dominic Ek Leong; Sanjayan, Jay; Nazari, Ali

doi:10.1016/j.conbuildmat.2015.12.141

Cited by 188 publications

(76 citation statements)

References 37 publications

(57 reference statements)

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“…The results pointed out that the highest average compressive strength was obtained in the specimens with a Na2SiO3/NaOH ratio of 2, while the lowest compressive strength was achieved on the specimens with a Na2SiO3/NaOH ratio of 2.5. The highest compressive strength of the specimens with a Na2SiO3/NaOH ratio of 2 was also obtained in the earlier investigation [20]. In addition, the maximum average compressive strength improvement (~122%) due to the oven-curing was obtained in the specimens with an alkali activator ratio of 1.5, while the least compressive strength improvement (~43%) was found in the specimens with an alkaline activator ratio of 2.5.…”

Section: Fig 5 Compressive Strengths Of the Alkali Activated Fly Assupporting

confidence: 65%

Compressive strength variation of alkali activated fly ash/slag concrete with different NaOH concentrations and sodium silicate to sodium hydroxide ratios

Niş¹

2019

jscmt

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Waste disposal becomes a crucial issue for both the environment and the economy. One of the solutions for waste disposal is to utilize waste materials in concrete production. Nowadays, alkali activ ated concrete takes attention since waste materials (fly ash and ground granulated blast furnace slag) are utilized instead of ordinary Portland cement as binder materials. In this study, alkali activated fly ash/slag concrete is produced using 50% F-type fly ash and 50% ground granulated blast furnace slag and the compressive strength of the alkali activated fly ash/slag concrete is evaluated. The sodium silicate (Na 2SiO3) and sodium hydroxide (NaOH) solutions were utilized with four different sodium silic ate to sodium hydroxide ratios (1, 1.5, 2, and 2.5) and three different molarities were utilized (6M, 10M, and 14M) for alkali activation to determine the effect of these parameters on the compressive strength of the alkali activated fly ash/slag concrete. In addition to ambient-curing (AC), the influence of the delayed oven-curing (OC) was also studied to determine the effect of curing regime on the compressive strength of the alkali activated fly ash/slag concrete. The results indicated that both the alkali activator ratio and NaOH concentration significantly affected the compressive strength of the alkali activated fly ash/slag concrete. In addition, the delayed oven-curing was also found as an important parameter for the compressive strength of the alkal i activated fly ash/slag concrete. Keywords:Alkali activated fly ash/slag concrete; sodium hydroxide concentration; molarity; fly ash and slag; sodium silicate to sodium hydroxide ratio. __________________________________________________________________________________________

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Section: Fig 5 Compressive Strengths Of the Alkali Activated Fly Assupporting

confidence: 65%

Compressive strength variation of alkali activated fly ash/slag concrete with different NaOH concentrations and sodium silicate to sodium hydroxide ratios

Niş¹

2019

jscmt

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“…45 Other researchers also indicate that excessive silicate from higher molar ratio of SiO 2 /Na 2 O may inhibit the geopolymerization due to the formation of aluminosilicate gel precipitation and further apart the aluminosilicate source and the alkali activators. [46][47][48][49][50] As shown in Figure 5b, the flexural strength of all three specimens tested increased as the curing time increased from 7 to 28 days. The flexural strength of M-0.96 and M-1.28 are very similar and much higher than that of M-1.91 specimen.…”

Section: Mechanical Strength Of Geopolymer Pastementioning

confidence: 78%

“…It can be attributed to the hydration of Ca species and the creation of a calcium–aluminum–silicate–hydrate (C–A–S–H) gel at very rapid pace, often resulting in a very short initial setting time during the early stage of geopolymeric reaction . Other researchers also indicate that excessive silicate from higher molar ratio of SiO 2 /Na 2 O may inhibit the geopolymerization due to the formation of aluminosilicate gel precipitation and further apart the aluminosilicate source and the alkali activators …”

Section: Resultsmentioning

confidence: 99%

Application of geopolymer paste for concrete repair

Ding

Cheng

Dai

2017

Structural Concrete

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In this study, ground granulated blast furnace slag and coal fly ash were used as raw materials to prepare geopolymer paste as repair material for concrete structure. The functional properties, such as compressive strength, fluxural strength, and bonding strength between slag/fly ash based geopolymer paste and paste substrate were investigated. The SiO2 /Na2O molar ratio of the alkali activator plays an important role on the strength of geopolymer paste. The nature of the geopolymeric reaction product was examined using FTIR and NMR. The compressive strengths and flexural strength of the geopolymer paste were 47 MPa and 16 MPa, respectively. For concrete substrate bonded with geopolymer paste, the compressive strength test shows up to 120% repairing rate can be achieved. By comparing with Portland cement, it can be proved that the slag/fly ash based geopolymer paste has very good potential for further engineering development in the future.

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“…The starting values for 3 levels of the parameters in Table were selected based on literature review (or our preliminary investigation). For instance, the 3 levels of NaOH/Na 2 SiO 3 molar ratio, 0.065, 0.265, and 0.465 were selected based on the literature review and the 3 levels of the Ca/Na molar ratio, that is, 4.29, 5.79, and 7.29, were inspired by our preliminary investigation.…”

Section: Methodsmentioning

confidence: 99%

High calcium cementless fly ash binder with low environmental footprint: Optimum Taguchi design

Hwang

Shahsavari

2018

J Am Ceram Soc

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Despite the myriad of research efforts on exploiting fly ash as an alternative binder, its current role in industry is largely restricted to the supplementary use, which enables only partial replacement of conventional portland cement. Herein, we propose an unprecedented binder composite with the promising early‐age strength, which is cost‐effective and reduces the CO2 footprint compared with portland cement. The major constituent is fly ash occupying 76.4%‐80.3% by the total mass of the constituents, while calcium oxide, nanosilica, and the minimum amounts of sodium‐based activators are added to induce the early‐age strength development. Optimization of the composition via the Taguchi design of experiments produced the early (7‐day) compressive strength of 16.18 MPa. This value is encouraging considering that it is comparable to that of conventional portland cement and that a cementless composition with the minimum amounts of sodium‐based activators was employed. The extensive materials analysis demonstrates that the starting Ca/Na molar ratio and the amount of nanosilica play instrumental roles in strength development by influencing the formation of key reaction products, which include the sodium‐substituted AFm phase (the U‐phase), katoite and portlandite. Overall, the promising early‐age strength coupled with the significantly decreased amount of sodium‐based chemicals and the reduced CO2 footprint will lay a foundation for development of low‐cost, environmentally friendly binder in diverse industries.

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The effect of different Na 2 O and K 2 O ratios of alkali activator on compressive strength of fly ash based-geopolymer

Cited by 188 publications

References 37 publications

Compressive strength variation of alkali activated fly ash/slag concrete with different NaOH concentrations and sodium silicate to sodium hydroxide ratios

Compressive strength variation of alkali activated fly ash/slag concrete with different NaOH concentrations and sodium silicate to sodium hydroxide ratios

Application of geopolymer paste for concrete repair

High calcium cementless fly ash binder with low environmental footprint: Optimum Taguchi design

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